Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2001-05-24
2003-05-27
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
Reexamination Certificate
active
06570529
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to determining the location of wireless mobile communication devices. More particularly, it relates to techniques for wireless location in an integrated system.
DESCRIPTION OF THE RELATED ART
One way to determine position or location of an object is through the use of Global Positioning Systems (GPS). Global positioning systems, which are satellite based, provide accurate, three dimensional position information to worldwide users.
FIG. 1
a
depicts a global positioning system (GPS)
10
. The GPS
10
comprises a plurality of satellites
12
-j and at least one GPS receiver
14
, where j=1, 2, . . . , n. Each satellite
12
-j orbits the earth at a known speed v
j
and is separated by a known distance from the other satellites
12
-j. Each satellite
12
-j transmits a global position signal
11
-j which includes a carrier signal with a known frequency f modulated with a unique pseudo-random noise (PN-j) code and navigational data (ND-j) associated with the particular satellite
12
-j. The PN-j code includes a unique sequence of PN chips and navigation data ND-j which includes a satellite identifier, timing information and orbital data, such as elevation angle &agr;
j
and azimuth angle &phgr;
j
.
FIG. 1
b
depicts a typical 20 ms frame of the GPS signal
11
-j which comprises twenty full sequences of a PN-j code in addition to a sequence of navigation data ND-j.
GPS receiver
14
comprises an antenna
15
for receiving GPS signals
1
-j, a plurality of correlators
16
-k for detecting GPS signals
11
-j and a processor
17
having software for determining a position using the navigation data ND-j, where k=1, 2, . . . , m. GPS receiver
14
detects GPS signals
11
-j via PN-j codes. Detecting GPS signals
11
-j involves a correlation process wherein correlators
16
-k are used to search for PN-j codes in a carrier frequency dimension and a code phase dimension. Such a correlation process is implemented as a real-time multiplication of phase shifted replicated PN-j codes modulated onto a replicated carrier signal with the received GPS signals
11
-j, followed by an integration and dump process.
In the carrier frequency dimension, GPS receiver
14
replicates carrier signals to match the frequencies of the GPS signals
11
-j as they arrive at GPS receiver
14
. However, due to the Doppler effect, the frequency f at which GPS signals
11
-j are transmitted changes an unknown amount &Dgr;f
j
before the signal
11
-j arrives at the GPS receiver
14
. Thus, each GPS signal
11
-j will have a frequency f+&Dgr;f
j
when it arrives at the GPS receiver
14
. To compensate for the Doppler effect, GPS receiver
14
replicates the carrier signals across a frequency spectrum f
spec
ranging from f+&Dgr;f
min
to f+&Dgr;f
max
until the frequency of the replicated carrier signal matches the frequency of the received GPS signal
11
-j, wherein &Dgr;f
min
and &Dgr;f
max
are a minimum and maximum change in the frequency the GPS signals
11
-j will undergo due to the Doppler effect as they travel from satellites
12
-j to GPS receiver
14
, i.e., &Dgr;f
min
≦&Dgr;f
j
≦&Dgr;f
max
.
In the code phase dimension, GPS receiver
14
replicates the unique PN-j codes associated with each satellite
12
-j. The phases of the replicated PN-j codes are shifted across code phase spectrums R
j
,(spec) until the replicated carrier signals modulated with the replicated PN-j codes correlate, if at all, with the GPS signals
11
-j being received by the GPS receiver
14
, where each code phase spectrum R
j
(spec) includes every possible phase shift for the associated PN-j code. When the GPS signals
11
-j are detected by the correlators
16
-k, GPS receiver
14
extracts the navigation data ND-j from the detected GPS signals
11
-j and uses the navigation data ND-j to determine a location for the GPS receiver
14
.
A GPS enables a ground based receiver to determine its position by measuring the time difference required for GPS signals initiated from two or more satellites to be received by the GPS receiver
14
. The pseudorange is defined as this time difference times the speed of light. The pseudorange is not the real range because it contains errors caused by the receiver clock offset. To determine a two-dimensional position (latitude and longitude) usually entails receiving signals from at least three satellites. To determine a three-dimensional position (latitude, longitude, and altitude) usually entails requires receiving pseudoranges from four or more satellites. This precondition, however, may not always be satisfied, especially when the direct satellite signals are obstructed, such as when a wireless terminal is inside a building.
GPS receivers, such as GPS receiver
14
, are now being incorporated into wireless mobile communication devices (including mobile telephones, PDAs, pagers, portable computers, etc.). However, these devices do not always have a clear view of the sky. In this situation, the signal-to-noise ratios of GPS signals
11
-j received by GPS receiver
14
are typically much lower than when GPS receiver
14
does have a clear view of the sky, thus making it more difficult for GPS receiver
14
to detect the GPS signals
11
-j.
Integrated wireless-global positioning (WGP) systems were developed to facilitate the detection of GPS signals by GPS receivers in wireless mobile communication devices. The WGP system facilitates detection of GPS signals by reducing the number of integrations to be performed by correlators searching for GPS signals. The number of integrations is reduced by narrowing the frequency range and code phase ranges to be searched. Specifically, the WGP system limits the search for GPS signals to a specific frequency or frequencies and to a range of code phases less than the code phase spectrum R
j
,(spec). However, problems of obstructed signals still exist. Further, an even greater problem involves the fact that many wireless mobile communication devices do not include any type of GPS receiver. These type of “legacy” devices, therefore, need to be located by some other measure.
Another known way of determining the position of a wireless mobile communication device is to utilize information obtained from a wireless network. One such method of geolocation uses signal strength measurements. In the IS136 and IS54 standards, signal strengths are extensively used for so-called MAHO (mobile-assisted handoff) process. The MAHO measurement contains signal strength information, which reflects the distance between the wireless terminal and a base station (BS). MAHO measurement lists are routinely delivered by wireless mobile communication devices for handoff purposes and form the basis of a low-accuracy geolocation system based on either, or a combination, of two techniques: “triangulation” and “contour matching”.
In the first technique, “triangulation,” the signal strength from multiple MAHO channels is associated with a location of a wireless mobile communication device. This then produces a geometric triangulation mathematical problem that can be solved to determine the location of the wireless mobile communication device (“wireless mobile”).
FIG. 2
illustrates a known method for determining a location from which a mobile caller originates a call on a wireless mobile
102
. Specifically, a signal originating from at least one base station, such as base station
104
, reaches the wireless mobile
102
with a particular signal strength at a particular time. Similarly, signals from base stations
106
and
108
send similar signals, which arrive at wireless mobile
102
at the same time but with varying signal strengths. In aIS136-based network, many such signals arrive at a given instant and their strengths are recorded for handoff purposes. Methods for using these data to determine such a location of the wireless mobile
102
are well-known and will not being further described for the sake of brevity.
In the second technique, termed “contour matching”, the wireless system receives
Budka Kenneth C.
Calin Doru
Jeske Daniel R.
Richton Robert E.
Harness Dickey & Pierce PLC
Lucent Technologies - Inc.
Phan Dao
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